All installations and services must be performed by qualified service personnel.
IS INDUCER RUNNING
ON LOW SPEED?
DOES THE HOT
SURFACE IGNITOR
ENERGIZE AND GLOW?
CHECK WIRING TO HOT
SURFACE IGNITOR AND
IF OK, REPLACE HOT
SURFACE IGNITOR
ASSEMBLY
AFTER HOT SURFACE
IGNITOR WARM-UP,
DOES GAS VALVE OPEN?
NO
NO
NO
NO
YES
YES
YES
CHECK CONTACTS ON LOW
FIRE PRESSURE SWITCH
AND FOR BLOCKAGE IN FLUE.
IF OK, REPLACE DUAL
PRESSURE SWITCH.
IS THE HIGH LIMIT,
ROLL-OUT LIMIT, AND
AUX LIMIT ON
(CDX MODELS)
SWITCHES CLOSED?
NO
YES
YES
IF HIGH LIMIT OR
AUX LIMIT OPEN CHECK
FOR RESTRICTED
FILTERS OR DUCT WORK
IF ROLL-OUT SWITCH
OPEN INSPECT FLUE FOR
RESTRICTIONS.
NO
CHECK WIRING TO GAS
VALVE AND IF OK,
REPLACE GAS VALVE.
IS COLLECTOR BOX
PRESSURE SWITCH CLOSED?
YES
YES
CHECK DRAIN FOR
BLOCKAGE WATER
TRAPPED IN HOSE,
REPLACE SWITCH.
NO
NO
AFTER GAS VALVE
OPENS, DO THE
BURNERS IGNITE?
YES
OK
CHECK FOR PROPER LINE
AND MANIFOLD PRESSURE.
REFERENCE GAS PRESSURE
CHART PAGE 31.
IS THERE VOLTAGE ACROSS
HOT SURFACE IGNITOR
TERMINALS "IGN" & "IGN N"
AT THE 50V51-843 CONTROL
AFTER 17 SECOND PREPURGE?
REPLACE THE
50V51-843 CONTROL.
CHECK ACROSS "MVL" AND
"MV COM" TERMINALS ON
50V51-843 CONTROL FOR 24
VOLTS DURING THE 4 SECOND
FLAME PROVING PERIOD
AFTER IGNITOR WARM-UP.
IS THERE 24 VOLTS?
REPLACE THE
50V51-843 CONTROL.
51
